Wafer Topography Measurement Offset Strategy
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Solution Overview
Problem
In the fabrication of NAND flash memory with a vertical structure, increased level differences on the wafer surface due to stacking lead to defocusing issues during the lithography process, necessitating accurate measurement of topographies to prevent focus errors.
Innovation Solution
An exposure apparatus with a measurement device and control system that sets offset measurement points on adjacent sections of the wafer, uses a focus sensor with a grating to acquire topography data, and performs interpolation to enhance measurement data density, enabling precise focus leveling control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement points are set at reference positions on each section, then measurement process is simple, but measurement data density is insufficient leading to defocusing
Solution Approach 1:
The patent transitions from one-dimensional measurement (single reference position per section) to two-dimensional measurement (multiple offset positions across adjacent sections). By distributing measurement points across both the first and second sections with offset positions, the system achieves higher measurement data density without simply adding more measurement points to a single location, thus improving topography measurement accuracy while maintaining a structured approach.
Solution Approach 2:
The measurement area is segmented into multiple sections (first section and second section) with distinct measurement points. Each section has its own reference position and offset positions, allowing independent measurement and subsequent interpolation. This segmentation enables comprehensive coverage of the wafer surface topography while maintaining manageable complexity in the measurement system.
2Measurement precision
If measurement points are increased in each section, then topography measurement accuracy improves, but measurement time and processing complexity increase
Solution Approach 1:
The patent combines measurement data from the first section and second section together through interpolation processing. By merging datasets from adjacent sections with offset positions, the system achieves enhanced measurement accuracy equivalent to having more points in a single section, but without the increased measurement time and processing complexity that would result from concentrating all measurement points in one location.
3Productivity
If focus leveling control is performed with limited measurement points, then processing is faster, but defocusing occurs due to insufficient measurement accuracy
Solution Approach 1:
The system performs preliminary interpolation processing to generate comprehensive topography data before focus leveling control. By pre-calculating the interpolated topography map from offset measurement points across adjacent sections, the system ensures high measurement accuracy is available when needed for focus leveling, without delaying the actual exposure processing. This preliminary action resolves the contradiction by preparing accurate data in advance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for high-accuracy measurement of wafer topographies, preventing defocusing and improving focus leveling control, even in sections with limited measurement points, thereby enhancing the exposure process's accuracy and convenience.
Implementation Method 1
a measurement device and a control device. The control device sets, on each of a first section and a second section adjacent to each other among the plurality of sections, a measurement point at a position offset from a reference position of each section. The control device causes the measurement device to measure surface information at each measurement point.
Data Source
AI summary
According to one embodiment, an exposure apparatus performs exposure to transcribe a circuit pattern onto each of a plurality of sections on a wafer. The exposure apparatus includes a measurement device and a control device. The control device sets, on each of a first section and a second section adjacent to each other among the plurality of sections, a measurement point at a position offset from a reference position of each section. The control device causes the measurement device to measure surface information at each measurement point. The control device executes focus leveling control for exposure on the basis of the surface information measured at each measurement point.